Editor's Note: Larry Schweiger is President and Chief Executive Officer of the National Wildlife Federation. The federation is a nonprofit organization that seeks to protect wildlife habitats and advocate for solutions to global warming.

Larry Schweiger says global warming is the defining issue of the 21st century.

(CNN) -- Nature can be amazingly resilient, capable of adapting to constantly changing ecological conditions. And yet, this resiliency is limited and rapidly reaching the breaking point.

In the lifetime of a child born today, 20 percent to 30 percent of the world's plant and animal species will be on the brink of extinction -- in part because of global warming -- if we fail to act.

Like it or not, global warming is the defining issue of the 21st Century. Climate scientists have issued warnings that we must act now to curb emissions of heat-trapping gases that cause global warming.

Dr. James Hansen of the National Oceanic and Atmospheric Administration has warned that the next two years are a "last chance" to act before we tip our climate system too far out of balance, creating a fundamentally "different planet."

Unchecked, we are heading to a full-blown climate crisis as the planet encounters several key tipping points including:

• Widespread damage to forests caused by expanded wildfire and insect infestation. A four-fold increase in the number of forest fires and a six-fold expansion of acres burned in the Western United States has been linked to global warming and drier conditions. Fires in Russia last summer consumed 29 million acres. Insect infestations have killed millions of acres of forests in North America as larvae increasingly survive warmer winters.

• Persistent drought. By the 2020s, 75 to 250 million people in Africa risk losing access to clean water, and some African countries are expected to see a 50 percent decline in crop yields.

• Flooding caused by rising sea levels will put hundreds of millions of people, including many Americans, at risk.

The acceleration of the Arctic ice melt is a powerful warning that we are rapidly running out of time. The last two summers have seen dramatic, record-shattering declines in the Arctic ice cap.

Not too long ago, scientists were concerned that global warming could completely melt the Arctic ice cap within a century. Today, some scientists are predicting that this may happen in five years. Polar bears are drowning and other sea life is struggling with the decline of Arctic ice.

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Arctic ice melt presents multiple dangers, including the release of methane. Vast quantities of methane, a greenhouse gas 25 times more potent than carbon dioxide, are stored in permafrost.

Melting of even a small fraction of this permafrost -- on land or the ocean floor -- and the subsequent release of methane could cause a runaway greenhouse effect. Scientists recently documented openings in the Arctic Ocean sea floor off the Siberian coast where millions of tons of methane are escaping.

This rapid ice melt is now creating an international fight for the oil that lies beneath the ice. The irony of this should not be lost. Oil is a top culprit in polluting our atmosphere with heat-trapping gases. Rather than fighting for more of the very resource that has created this climate crisis, countries should be working together to do everything possible to prevent further melting.

Fortunately, America is ready to act. President-elect Barack Obama has stated that we are entering "a new chapter in America's leadership on climate change." He recognizes the economic opportunity to create jobs and reduce our dependency on oil by investing in the clean energy technologies that will safeguard our planet.

We need a green shovel to dig our way out of our economic hole. The investments in clean energy that forestall a climate meltdown will aid our recovery from the global financial meltdown.

Overwhelming numbers of Americans are ready. According to election polling, more than three-quarters of voters are demanding a shift toward clean energy in order to revitalize America's economy.

And yet, the clean energy revolution will not be a sufficient response to the climate crisis. We must also protect the nature of tomorrow in the face of this threat. Safeguarding wildlife and protecting natural resources in a warming world requires bold approaches to natural resource management that will transform the way we approach wildlife conservation.

The eyes of the world are upon America and what we do this coming year. In 2009, we need to enact a federal program to promptly cap and reduce the pollution causing global warming at the pace scientists tell us is needed. We must use the financial resources from this program to invest in clean energy technologies, safeguard America's natural resources and protect communities from the threats of a destabilized climate.

With renewed U.S. leadership, we can secure an effective global agreement on climate change that engages every nation around the world in the effort to protect our planet, and ourselves.

Conflicts over natural resources are accelerating, and we must address the imperative of balancing human needs with the natural world. We can no longer afford to separate the two -- we all depend on healthy natural resources for the food we eat, the water we drink, the houses we build -- no matter where we live.

After all, we have only one planet. And good planets are hard to find.

The opinions expressed in this commentary are solely those of Larry Schweiger.